Floristic composition, structure, and dynamics of an upper montane rain forest in Southern Ecuador

Two 1 ha plots of undisturbed upper montane rain forest in southern Ecuador were sampled for all trees with a dbh ≥ 5 cm. An extraordinarily high α-diversity for a forest near treeline is described. The "non-ridge forest" plot at 2900 m elevation has 75 species and 28 families ha^-1 and is believed to represent an advanced stage of succession whereas, the "ridge forest" plot at 2700 m elevation with 90 species and 38 families ha^-1 has a more rapid turn-over rate probably due to a more unstable environment. Downslope forces (soil creep) are discussed as a possible cause for 32–44% of all trees being inclined more than 30° in the moderately steep terrain (average slope 20° in both study plots). The plot of "non-ridge forest" is characterized by a much greater biomass whether expressed as basal area (44 m² versus 15 m²) or stem volume (214 m³ versus 52 m³), while the density is equally high (2310 versus 2090 trees ha^-1) in both plots. Families with Family Importance Value >25 / ha^-1 are Clusiaceae, Cunoniaceae, Melastomataceae, Myrsinaceae, and Ternstroemiaceae.     

Effects of glyphosate on nitrogen fixation of free-living heterotrophic bacteria

The effect of the herbicide glyphosate ( N -(phosphonomethyl)glycine) on the growth, respiration and nitrogen fixation of Azotobacter chroococcum and A. vinelandii was studied. Azotobacter vinelandii was more sensitive to glyphosate toxicity than A. chroococcum. Recommended dosages of glyphosate did not affect growth rates. More than 4 kg ha^-1 is needed to find some inhibitory effect. Specific respiration rates were 19.17 mmol O₂ h^-1 g^-1 dry weight for A. chroococcum and 12.09 mmol h^-1 g^-1 for A. vinelandii. When 20 kg ha^-1 was used with A. vinelandii , respiration rates were inhibited 60%, the similar percentage inhibition A. chroococcum showed at 28 kg ha^-1. Nitrogen fixation dropped drastically 80% with 20 kg ha^-1 in A. vinelandii and 98% with 28 kg ha^-1 in A. chroococcum. Cell size as determined by electron microscopy decreased in the presence of glyphosate, probably because glyphosate induces amino acid depletion and reduces or stops protein synthesis.     

In situ responses to elevated CO2 in tropical forest understorey plants

1. Plants growing in deep shade and high temperature, such as in the understorey of humid tropical forests, have been predicted to be particularly sensitive to rising atmospheric CO₂. We tested this hypothesis in five species whose microhabitat quantum flux density (QFD) was documented as a covariable. After 7 (tree seedlings of Tachigalia versicolor and Beilschmiedia pendula ) and 18 months (shrubs Piper cordulatum and Psychotria limonensis, and grass Pharus latifolius ) of elevated CO₂ treatment ( c. 700 μl litre^–1) under mean QFD of less than 11 μmol m^–2 s^–1, all species produced more biomass (25–76%) under elevated CO₂.
2. Total plant biomass tended to increase with microhabitat QFD (daytime means varying from 5 to 11μmol m^–2 s^–1) but the relative stimulation by elevated CO₂ was higher at low QFD except in Pharus .
3. Non-structural carbohydrate concentrations in leaves increased significantly in Pharus (+ 27%) and Tachigalia (+ 40%).
4. The data support the hypothesis that tropical plants growing near the photosynthetic light compensation point are responsive to elevated CO₂. An improved plant carbon balance in deep shade is likely to influence understorey plant recruitment and competition as atmospheric CO₂ continues to rise.     

Standing crop and distribution of fish in drifting and attached floating meadow within an Upper Amazonian varzea lake

The standing crop and distribution of fish within the floating meadow habitat of Lago Mamirauá, an upper Amazonian floodplain lake, were studied during December 1993 when the water was rising and had just begun to enter the forest. The ichthyofauna was dominated by six groups, the Anostomidae, Gymnotiformes, Erythrinidae, Serrasalmidae, Synbranchidae and Cichlidae. For anchored meadow, total wet weight was estimated as 312 kg ha ^-1 and total number as 90 400 individuals ha^-1. This biomass estimate was probably below the annual maximum because some fish had already dispersed into the forest, but, the number of individuals was close to the annual maximum because of the recent arrival of juvenile Serrasalmidae and Cichlidae. For drifting islands of meadow fish biomass and density were estimated as 192kg ha^-1 and 12 700 individuals ha^-1 respectively. The Synbranchidae, Gymnotiformes and Erythrinidae avoided drifting meadow. In comparison, the Cichlidae and Anostomidae, while favouring marginal, anchored meadow, were frequently dispersed by drifting islands. The Siluriformes were unique in favouring drifting over anchored meadow. For this group the observed down-stream drift may be a seasonal migration to the main river channels. Juvenile fish avoided drifting islands, presumably to avoid being flushed from the lakes. Their abundance was lowest at the mouth of the lake. The generally abundant Serrasalmus spp. juveniles were absent from meadow at the mouth of the lake.     

The effect of beet cyst nematode, Heterodera schachtii, on the yield of sugar beet in organic soils

In ten experiments on commercial sugar-beet crops grown on organic soils in 1984–86, a Genstat programme was used to examine the relationship between the initial population of Heterodera schachtii and sugar-beet root yield using the equation
Y = Ymin + (Ymax - Ymin) Z^pi-T
Fixing T = 200 eggs + juveniles 100 g^-1 soil and Z^T= 0.95, estimated values of Ymax varied from 49.2–67.1 t ha^-1 (129– 155% of the national average root yield for the years in which the experiments were carried out) and estimates of Ymin varied from 14.5–53.9 t ha^-1 (27–94% of Ymax). The estimated average root yield loss caused by the nematode was 6.95 t ha^-1.     

Propagule pressure and resource availability determine plant community invasibility in a temperate forest understorey

Few field experiments have examined the effects of both resource availability and propagule pressure on plant community invasibility. Two non-native forest species, a herb and a shrub ( Hesperis matronalis and Rhamnus cathartica , respectively), were sown into 60 1-m² sub-plots distributed across three plots. These contained reconstructed native plant communities in a replaced surface soil layer in a North American forest interior. Resource availability and propagule pressure were manipulated as follows: understorey light level (shaded/unshaded), nutrient availability (control/fertilized), and seed pressures of the two non-native species (control/low/high). Hesperis and Rhamnus cover and the above-ground biomass of Hesperis were significantly higher in shaded sub-plots and at greater propagule pressures. Similarly, the above-ground biomass of Rhamnus was significantly increased with propagule pressure, although this was a function of density. In contrast, of species that seeded into plots from the surrounding forest during the growing season, the non-native species had significantly greater cover in unshaded sub-plots. Plants in these unshaded sub-plots were significantly taller than plants in shaded sub-plots, suggesting a greater fitness. Total and non-native species richness varied significantly among plots indicating the importance of fine-scale dispersal patterns. None of the experimental treatments influenced native species. Since the forest seed bank in our study was colonized primarily by non-native ruderal species that dominated understorey vegetation, the management of invasions by non-native species in forest understoreys will have to address factors that influence light levels and dispersal pathways.     

Ranging behaviour and foraging habitats of breeding Sparrowhawks Accipiter nisus in a continuous forested area in Norway

The ranging behaviour and foraging habitats of Sparrowhawks Accipiter nisus were studied in a continuous forest area in southern Norway by use of radiotelemetry in 1995 and 1996. The mean size of the home ranges was 9.2 km² for males (sd ± 3.7, n = 6) and 12.3 km² for females (sd ± 6.4, n = 6), but the difference was not significant. Females ranged farther away from nests (mean 1824 m) than did males (mean 1240 m). None of the Sparrowhawks were located outside forest habitats. For the three pairs where both mates were radiotracked in 1996, habitat use did not differ between the sexes. Habitat composition in the home ranges differed from that of the study area. The most important difference was a higher proportion of medium-aged forest and a lower proportion of old forest in home ranges than in the study area. The selection for medium-aged forests was probably a response to high food supply and good hunting opportunities. Mixed regeneration and old forests were used more than clear-fell areas, which were seldom used. Mixed regeneration was also used more than coniferous replanting. The large home ranges in this study compared with those in studies in Great Britain is probably due to lower land productivity and associated lower densities of prey species in the present study. The study indicates that the Sparrowhawk benefits from modern forestry, which has created an increased proportion of medium-aged stands in the forest landscape.     

Influence of habitat characteristics on small mammals in a Mexican high-altitude grassland

Small mammals in a high-altitude grassland area close to Mexico City were studied. Populations of 10 species were censused using live traps in 48 sample quadrats. Within each quadrat, vegetation characterization, including complete floristic listings, cover values for species and layers and values of habitat modification, were assessed. Habitats were described according to plant communities identified using ordination and classification methods. Nine different plant communities were obtained. Densities and abundance of all small mammal species were calculated for each of the habitats classified. Peromyscus alsloni was the most abundant species in all habitats, reaching maximum densities of 55 ha⁻¹ in pine forest with dense ground and herb layer. Peromyscus melanotis also occurred in all habitats but at lower densities (maximum 29 ha⁻¹). Reithrodontomys megalotis was found in all habitats except in tall dense grassland. Densities for this species were generally low (1-9 ha⁻¹) but reached 19 ha⁻¹ in short dense grassland. All other species were largely absent from 4–8 habitats and showed very low densities (0.75–4 ha⁻¹). The densities of the more abundant species were largely correlated with more open habitats and higher indices of habitat modification. Lower altitude grassland habitats have a greater abundance of small mammals and a higher species richness than the medium and higher altitude, physiognomically more complex habitats. Species richness was highest in tall pine-alder forest with a species-rich, dense herb layer and lowest in pine forest with dense ground and herb layers. Species richness was positively correlated with overall small mammal density.     

Successional trends in the energetics of forest bird communities

Thirty forest bird communities were studied with regard to the changes in structural indices (number of species, density, biomass, species diversity H') and in energetics (energy flow A, production P, ecological efficiency P/A) in temporal and spatial gradients. All these characteristics increase during temporal succession; in natural deciduous forest there is a two-peak pattern of the increase, with the maximum in 15–20 yr old forest ("time ecotone"; A = 692.9 Megajoules ha⁻¹ season⁻¹, H'= 4.2 bits), In artificially managed pine forest these indices rise monotonically, reaching a maximum in sub-climax (A = 426.2 MJ ha⁻¹ season⁻¹, H'= 4.2 bits). In a deciduous forest a tendency exists to decrease the ecological efficiency (from 8% to 2%), while in a coniferous stand this variable remains low (2%) and almost constant during succession. In a spatial gradient, the highest values of energy flow and species diversity occur in forest stands with moderate soil/water regime and of ecotonal character (A = 851.2 MJ ha⁻¹ season⁻¹, H'= 4.5 bits). All mature forest bird communities show similar values of diversity (4.2–4.5 bits) and ecological efficiency (appr. 2%), though they differ in the rate of energy flow. The relation of these findings to the current concepts of ecological succession are discussed.     

Cadmium and copper change root growth and morphology of Pinus pinea and Pinus pinaster seedlings

Heavy metal loads in forest soils have been increasing over time due to atmospheric inputs. Accumulation in the upper soil layers could affect establishment of seedlings and forest regeneration. Mediterranean species show a high initial root development, allowing seedlings to reach the moisture of deeper soil layers. In the present work seedlings of stone pine ( Pinus pinea L.) and maritime pine ( Pinus pinaster Ait.), were grown in culture solution supplied with 0.0, 0.1, 1 or 5 μ M CdSO₄ or with 1 μ M CdSO₄ and 1 μ M CuSO₄ combined. In both species tap-root elongation was drastically reduced in the 5 μ M Cd²⁺ and in the (Cd²⁺+ Cu²⁺) treatments. A supply of 0.1 or 1 μ M Cd²⁺, however, enhanced root elongation in Pinus pinea without significantly influencing root elongation in Pinus pinaster . In both species the root density (weight per unit length) and the width of the cortex increased in response to Cd²⁺ exposure. In Pinus pinaster the mitotic index decreased at the higher Cd²⁺ concentrations and when Cd²⁺ and Cu²⁺ were combined. The data suggest that cell elongation is more sensitive to Cd²⁺ than cell division. The number and length of the lateral roots were also affected by Cd²⁺ treatment to a higher degree in Pinus pinaster than in Pinus pinea, reflecting the different Cd- tolerance of the two species.     

Maternal effects in progeny of field pansy (Viola arvensis) subjected to different herbicide and nitrogen rates

Observations were made on the effects of reduced rates of herbicide and nitrogen on naturally occurring populations of Viola aruensis. Progeny arising from these plants were grown in a uniform environment and monitored through to maturity. The size and number of reproductive structures produced by the maternal plants were positively correlated with the maternal plant weight. Herbicide dose affected the plant height of offspring and the effects were more pronounced in those from plants which had received 160 kg N ha^-1than 40 kg N ha^-1. Although the maternal effects on offspring size diminished with time, the number of reproductive structures in the offspring was significantly correlated with plant height during early development. Increased nitrogen availability to the maternal plant in the absence of herbicide may therefore increase the overall productivity of the subsequent generation.     

Effects of simulated N deposition on understorey vegetation of a boreal coniferous forest

1. We report the short-term effects of simulated nitrogen (N) deposition on the understorey of a boreal forest in northern Sweden. Doses of ¹⁵N double-labelled NH₄NO₃ (0·5, 12·5, 25·0 and 50·0 kg N ha^–1) were applied to 1 m² plots in the summer of 1995 and plants were harvested the following autumn.
2. No significant treatment effects were found in either above- or below-ground biomass which was distributed as follows: the ericaceous shrub Vaccinium myrtillus contributed 76%, the grass Deschampsia flexuosa 4%, and the bryophytes Dicranum majus and Pleurozium schreberi 20%.
3. The recovery of applied N in these species was 24, 27, 27 and 32% of the 0·5, 12·5, 25·0 and 50·0 kg N ha^–1 applications, respectively, and thus the recovery increased with the N dose.
4. In the 0·5 kg N ha^–1 treated plots, the highest concentrations of fertilizer-derived ¹⁵N were found in the bryophytes, while in plots given the three higher N applications, leaves of D . flexuosa had the highest concentrations.
5. N application resulted in elevated concentrations of free amino acid N, which indicate increased storage of N in plant tissues. Furthermore, the N application resulted in increased damage to V . myrtillus by natural enemies. The severity of disease caused by two foliar parasitic fungi showed a clear numerical response to N treatment, as did the amount of herbivory as a result of Lepidoptera larvae.     

The Impact of Sheep Grazing on Net Nitrogen Mineralization Rate in Two Temperate Salt Marshes

Abstract: Nitrogen mineralization rate was studied in grazing trials with three different stocking rates (0, 3, 10 sheep ha^-1) in two man-made salt marshes, viz. a Puccinellia maritima -dominated low salt marsh and a high salt marsh dominated by Festuca rubra. Mineralization rates were derived from the amounts of mineral N which accumulated in situ during six-week incubation periods in tubes containing undisturbed soil cores from the upper 10 cm soil layer. The annual rates of net N mineralization were significantly higher in the better drained, high salt marsh (71 - 81 kg ha^-1 yr^-1) than in the low salt marsh (39 - 49 kg ha^-1 yr^-1). High amounts of belowground litter accumulated in the low salt marsh due to frequent water logging. Both N mineralization and nitrification rate were negatively correlated with soil water content. In the Puccinellia maritima salt marsh, grazing had neither an effect on N mineralization rates during any of the incubation periods nor on annual mineralization rates. In the Festuca rubra salt marsh, N mineralization rates increased earlier during spring at the intensively grazed site than at the moderately grazed and the ungrazed site. N mineralization and nitrification rates were significantly higher at the ungrazed site than at the intensively grazed site during the period of peak net N mineralization from the end of April until mid-June. Although sheep grazing affected the seasonal pattern of N mineralization in the high marsh, grazing did not affect the annual rate of net N mineralization.     

Influence of soil applied nitrogen (NPKS 25: 5: 5:5) on Brevipalpus phoenicis Geijskes (Acari: Tenuipalpidae) mite incidence and damage symptoms on tea

Application of nitrogenous fertilisers (NPKS 25: 5: 5:5) for yield of tea and to induce tolerance to the red crevice ( Brevipalpus phoenicis Geijskes) mite was found to be rates between 150 and 200 Kg N ha^-1 yr^-1 rates above 400 Kg N ha^-1 encouraged the build up of mites on tea. Damage symptoms resulting from mite infestation declined with increase in application of nitrogenous fertilisers.
The levels of nitrogen in the leaf tissues increased with soil applied nitrogen and also was related to the mite numbers found on the leaves suggesting a link. The symptoms of the discoloured necrotic leaf base that accompanied mite infestation was significantly ( P ≤ 0.05) and linearly correlated (r = 0.60) to mite numbers in the control plot. The levels of applied nitrogen were negatively correlated to % leaf necrosis suggesting a tolerance leading to reduction in necrotic symptoms with fertiliser applications.     

Differential response of Trifolium species to 4-(2,4-dichlorophenoxy)butyric acid treatments

The differential response of white clover ( Trifolium repens L. cv. Regal Ladino) and berseem clover ( Trifolium alexandrinum L. cv. Mississippi ecotype) was investigated by treating greenhouse cultured plants with 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB). Berseem clover plants were significantly injured by a treatment concentration of 0.6 kg ha^-1 of 2,4-DB, whereas white clover plants were not injured by treatment levels below 2.4 kg ha^-1. The metabolism of 2,4-DB in cell suspension cultures of white clover and berseem clover was investigated using [ring-¹⁴C]-2,4-DB and non-labeled 2,4-DB. White clover cell cultures metabolized ca 4-fold more 2,4-DB than berseem cultures over a 44-h treatment period. The decrease in berseem cell population was 4-fold greater than the decrease in white clover cell population in response to the 8 μ M 2,4-DB treatment. The herbicide and its [ring-¹⁴C]-labeled metabolites were isolated from treated cells and medium after 44 h by partition and thin-layer chromatography. White clover cells metabolized 90% of the [¹⁴C]-2,4-DB and berseem clover cells metabolized 22% of the herbicide. The major portion of the radiolabel was in the glycoside fractions from extracts of both species. The differential response of Trifolium species to 2,4-DB is implied to be due to the differential rate of 2,4-DB metabolism to a glycoside by the clover plants.     

Small-scale patterns of species richness in Swedish semi-natural grasslands: the effects of community species pools

Temperate semi-natural grasslands are known for their high plant species richness at small spatial scales. We examined the variation in small-scale species richness in a sample of 63 sites from Swedish semi-natural grasslands, located as fragments in the modem landscape dominated by forest and agricultural land. Data were obtained from two spatial scales at each site. 1 dm² and 4 m². Using an analysis based on a Monte Carlo simulation, we found support for the species-pool hypothesis: a high species richness at the I dm- scale was associated with high species richness at the 4 m2 scale. The conclusion from this pattern analysis would, however, be considerably strengthened if we could reduce the likelihood that other mechanisms than sampling from species pools of unequal size influence the pattern of small-scale species richness. Additional analyses were made in order to identify such mechanisms. We examined whether four putative key traits: seed size, seed production, plant size and reproductive allocation were different among species at comparatively species-rich vs species-poor I dm' plots. We found only a little evidence for such differences. There was a weak tendency that species in the plots with high species richness possessed larger (and fewer) seeds than species from species-poor plots. Our results are congruent with the main prediction of the species pool model: variation in small-scale species richness (1 dm²- scale) is basically a result of sampling from unequally sized community species pools (4 m² scale). Variation in species richness between the 4 nr semi-natural grassland "patches" may thus be sought for among mechanisms operating al larger spatial scales than 4 m². We briefly discuss such mechanisms, based on other studies performed in the same study area.     

Development of selective aphicide treatments for integrated control of summer aphids in winter wheat

Field experiments on the use of recommended and reduced application rates of aphicides for control of summer aphid infestations on winter wheat have been done at five sites each year from 1990 to 1992. The experiment compared sprays of pirimicarb at recommended rate (140g a.i. ha^-1) and reduced rate (25 g a.i. ha^-1) and of alphacypermethrin at recommended rate (15 g a.i. ha^-1) and one third recommended rate (5 g a.i. ha^-1), each applied either at flag leaf emergence or at flowering. Aphid infestations were allowed to develop naturally and were measured at critical growth stages. In 1990, overwintered aphid infestations, together with established populations of parasitoids, were detected at four of the five sites when the first assessment was made in April. Parasitoids provided sufficient aphid control to prevent yield loss at two sites, without pesticide applications. At three sites both aphicides gave similar levels of control and yield response at both recommended and reduced application rates. In 1991 and 1992 no overwintered aphids were detected in the crops and aphid infestations developed much later. Aphicide applications gave significant yield responses at four sites in 1992. Recommended rates gave better control of aphids than reduced rates. There was no significant difference in the yield response obtained with different rates of aphicide.     

2006—2017年长白山阔叶红松林木本植物种子雨的时空动态

种子是森林更新的基础.为研究长白山阔叶红松林种子雨组成及时空变化,在长白山阔叶红松林25 hm²样地内设置150个面积为0.5 m²的收集器.自2006年5月至2017年12月收集252次,共收集到成熟、未成熟种子764299粒,隶属12科17属27种,其中,主林层树种13种704231粒,占总数的90%以上.种子最多的4个树种依次为紫椴、水曲柳、色木槭、假色槭,每年各个收集器都收集到这4个树种的种子;种子雨大爆发现象在各林层树种均存在,次林层和林下层较主林层树种滞后1~2年;各林层树种集中在秋季产生种子,各树种的种子雨都存在较大的时空变异性,相对而言,多数树种的空间变异性大于时间变异性;与科罗拉多岛(BCI)热带森林样地和浙江古田山亚热带常绿林样地种子产量的年际变异系数相比,长白山阔叶红松林种子产量年际变异系数较大,支持高纬度地区种子产量变异性高于低纬度地区的假说.     

Control of stem nematode, Ditylenchus dipsaci, in onions, by granular nematicides applied to the soil

Aldicarb at 1.4–5.6 kg a.i. ha^-l or oxamyl at 1.3–5.2 kg a.i. ha^-1 applied over the seed furrows during sowing prevented much of the damage resulting from stem nematode attack in spring-sown onions. Rotting of bulbs in store due to stem nematode infestation was sometimes lessened by these treatments. Neither sowing onion seeds on soil ridges, nor applying aldicarb in two equal doses, one over the seed furrows during sowing, the other over the plants mid-season, controlled the nematode better or increased onion yields more than a single equivalent dose over the seed furrows. Applied as two doses in this way, aldicarb was sometimes more effective against the nematode in summer-sown onions than was an equivalent amount applied over the seed furrows during sowing. Only 2.5 kg or less aldicarb ha^-1 can be applied to onions without leaving unacceptable residues (>0.15 μg g^-1) in the harvested bulbs.     

Home range and habitat use of wolverines Gulo gulo in Yukon, Canada

Home ranges and habitat use are described for three adult female, one adult male, and one subadult male wolverines in the Kluane Game Sanctuary, Yukon. When long distance excursions are not included, home ranges of wolverines in the Kluane Game Sanctuary were between 76 and 269 km² for females and 209 and 269 km² for males. Habitat use of females was similar to habitat availability. Males used subalpine coniferous habitats more frequently than other habitat types during winter. Although individual variation in the use of forest cover types, aspects, slopes and elevations was apparent, seasonal use did not differ from availability for each sex. Within the 1590 km² study area, three adult males and six adult females were present, corresponding to a density of one resident wolverine 177 km^-2.